1. Field of the Invention
This invention concerns knitting needles used in automatic knitting machines. In particular, this invention relates to a knitting needle capable of making hosiery, underwear fabric, outerwear fabric and industrial fabric.
2. Discussion of the Related Art
There are many known types of knitting needles which include latches. A common problem in knitting with conventional latch needles in automatic knitting machines is the spearing of the yarns when the stitch closes the latch before being cast off. In order to understand the source of this problem, a brief description of the knitting cycle follows.
A new yarn is laid under the hook of the needle by moving the needle into a position so that the hook passes the yarn carrier with the latch in the open position. The sideways motion of the needle accomplishes this positioning. The stitch of the previous course (the old stitch) is located on the blade or round out of the needle. The needle is then pulled backwards. The old stitch slides under the tip of the latch and moves the latch into the closed position. In the next part of the cycle, the new stitch opens the latch. In most instances, the tip of the latch is away from the blade of the needle and the old stitch has no problem sliding under the latch to close it. In some instances, however, the old stitch will not be able to slide under the latch and a problem commonly referred to as "spearing" occurs. "Spearing" especially occurs when needles have been used for a while and the latch seat has been worn deeper. The latch seat becomes particularly worn when knitting Lycra yarns, but does occur in all knitting situations.
Spearing can cause two different types of defects. First, it can jam the knitting cycle and permanently damage the knitting needle or, there may be a complete or partial dropped stitch depending on how much of the yarn in the old stitch climbs above the needle and how much of the old stitch slides under the latch.
When the needle is moved backwards, the old stitch is under considerable tension caused by the friction between steel and yarn. This tension contributes to the above-noted problem of spearing when the old stitch comes in contact with the sharp point of the latch.
Other concerns that arise are yarn breakage due to the high tension in the loop when the needle is moving backwards. Furthermore the yarn tension increases when the stitch or loop has to travel over an increased cross-section of the needle. The higher the tension in the loop the firmer the contact with the latch and hence an increased latch speed closing when contact occurs.
When the latch tip makes contact with the hook tip it bounces back until the stitch forces it back down again. This bouncing particularly with lighter yarn can interfere with a smooth cast off. This can affect fabric quality and even lead to yarn malfunctions and fabric faults.
Another problem which arises is with the pickup clearance of the needle. The pickup clearance of a needle is determined by the size of the yarn. Generally, the larger the yarn size, the higher the pickup clearance required. If there is not a sufficient pickup clearance, the yarn will snag on the latch rather than slip under the latch as necessary. As a result, an unwanted tuck stitch will occur, the needle will jam, and/or the stitch will be damaged.
Previous attempts to solve these problems have been to reduce the roundout height and/or increase the cheek height. However, increasing the cheek height forces the stitch into undesirable degrees of stretch. Additionally, reducing the blade height or roundout height for some distance reduces the resistance to flexing when the needle is in the raised position.